The major aim of this project is to develop and standardize an ELISA assay that measures IgG antibody (Ab) specific for the Group B streptococcus (GBS) capsular polysaccharide ( PS). To determine the best method for measuring specific IgG Ab to GBS Ps, we are comparing four different ELISA methods. The Ab values estimated were quite different among methods for GBS III. The GBS III polysaccharide is unique in that the same PS also has the pnmeumococcal type 14 immunodeterminant. Direct Ps binding and the mHSA methods measured similar IgG concentrations while the biotin and the HSA-conjugated methods estimated different, but similar IgG values. Competitive inhibition and absorption data demonstrated that biotin and HAS-conjugated methods also measure antibodies to the pneumococcal type 14 determinant in addition to the sialic acid dependent GBS III determinant. Since we are interested in specifically measuring GBS IgG antibodies that correlate with protection, we will determine which ELISA method agrees best with opsonophagocytic antibodies. Preliminary ELISA results with GBS type 1a indicate that all four methods give the same antibody concentrations. We are also developing an ELISA inhibition method to serotype GBS strains isolated from neonates.